Method and system for flattening hierarchically structured flows

ABSTRACT

There is disclosed a method and system for flattening hierarchically structured flows using a breadth-first approach. At each level of hierarchy of a hierarchically structured source flow, complex nodes are flattened by one level across the entire breadth of the flow. The results of this flattening are placed in a target flow, and any connections that existed in the source flow are re-established in the target flow in such a way that any data input into the target flow will be processed as if it had been input into the source flow. After a processing iteration, if there are still complex nodes remaining in the target flow, the target flow becomes the next source flow, and the process is repeated until the flow has been completely flattened.

A portion of the disclosure of this patent document contains materialwhich is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND

The present invention relates to software compilers, and moreparticularly to a method and system for flattening hierarchicallystructured flows commonly found in flow programming.

Flow programming involves modeling data flows through an arrangement ofnodes and connectors. The interconnected arrangement of nodes and thedata flows passing through the arrangement are referred to collectivelyas a “flow”.

In flow programming, applications may be built from a set of buildingblocks comprising different types of “primitive” nodes and connectors.In the context of the present discussion, primitive nodes are nodes thatcannot be “flattened” further (as detailed below). To support a morecompact hierarchical structure, “complex” nodes may be introduced. Acomplex node contains one or more “subflows”, where each “subflow” maycomprise one or more nodes. The one or more nodes in each subflow mayeither be a primitive node or another complex node having its ownsubflow or subflows. In this manner, a multi-level hierarchicalstructure of virtually any size may be built.

While it may be convenient to use a hierarchical structure to model aflow, it is not always possible to maintain such a structure. Forexample, in an application involving a transaction between two disparatesystems, one system may not be able to understand a hierarchicallystructured flow built in another system, and vice versa. In this case,it may be necessary to convert the hierarchically structured flow intoan equivalent flat flow which performs in essentially the same way asthe hierarchically structured flow. This flat flow may then be deployedinto an intermediary system acting as a broker between the disparatesystems.

Known techniques for flattening hierarchically structured flows aregenerally functional, but may be inefficient when used with certaintypes of hierarchically structured flows. In particular, a moreefficient technique is needed for flattening hierarchically structuredflows having significant breadth.

SUMMARY OF THE INVENTION

The present invention provides a method and system for flatteninghierarchically structured flows using a breadth-first approach.

At each level of hierarchy of a hierarchically structured source flow,complex nodes are flattened by one level across the entire breadth ofthe flow. The results of this flattening are placed in a target flow,and any connections that existed in the source flow are re-establishedin the target flow in such a way that data input into the target flowwill be processed as if it had been input into the source flow. After aprocessing iteration, if there are still complex nodes remaining in thetarget flow, the target flow becomes the new source flow, and theprocess is repeated until the flow has been completely flattened.

In an embodiment of the invention, there is provided a computersystem-implemented method of flattening a hierarchically structuredsource flow, the source flow including at least two levels of hierarchywith each level of hierarchy including one or more nodes interconnectedby connectors, the computer system-implemented method comprising:

-   -   (i) identifying, at a current top level of hierarchy in the        source flow, any primitive node;    -   (ii) adding to a target flow the primitive node identified in        (i);    -   (iii) identifying, at the current top level of hierarchy in (i),        any complex node, each complex node containing at least one        subflow with one or more nodes interconnected by connectors;    -   (iv) adding to the target flow the at least one subflow in place        of the complex node identified in (iii);    -   (v) re-establishing connections between any nodes and subflows        added to the target flow, and maintaining node terminal        connections such that any data flowing through the target flow        is processed as if through the source flow.

In an embodiment, the computer system-implemented method furthercomprises:

-   -   (vi) identifying whether there are remaining complex nodes in        the target flow, and if so, providing an indication thereof.

In another embodiment, the computer system-implemented method furthercomprises:

-   -   (vii) responsive to the indication of remaining complex nodes in        the target flow, defining the target flow to be a new source        flow, defining a new target flow, and repeating each of (i)        to (v) for the new source flow.

In another embodiment, at (v), re-establishing connections between anynodes and subflows added to the target flow proceeds as follows:

-   -   a connection in the source flow that connects an origin        primitive node to a destination primitive node is re-established        in the target flow without modification;    -   a connection in the source flow that connects an origin        primitive node to a destination complex node is replaced in the        target flow by a re-established connection that connects the        origin primitive node to a node in each subflow that was        previously connected to an input node of the destination complex        node;    -   a connection in the source flow that connects an origin complex        node to a destination primitive node is replaced in the target        flow by a re-established connection that connects a node in each        subflow, that was previously connected to an output node of the        origin complex node, to the destination primitive node;    -   a connection in the source flow that connects an origin complex        node to a destination complex node is replaced in the target        flow by a re-established connection that connects a node in each        subflow that was previously connected to an output node in the        origin complex node, to a node in each subflow that was        previously connected to an input node in the destination complex        node.

In another embodiment, the computer system-implemented method furthercomprises:

-   -   (vi) identifying whether there are remaining complex nodes in        the target flow, and if so, providing an indication thereof.

In another embodiment, the computer system-implemented method furthercomprises:

-   -   (vii) responsive to the indication of remaining complex nodes in        the target flow, defining the target flow to be a new source        flow, defining a new target flow, and repeating each of (i)        to (v) for the new source flow.

In another aspect of the invention, there is provided a computer systemcomprising a processor and computer readable memory, the memory storingsoftware for flattening a hierarchically structured source flow, thesource flow including at least two levels of hierarchy with each levelof hierarchy including one or more nodes interconnected by connectors,the software adapting the system to:

-   -   (a) identify, at a current top level of hierarchy in the source        flow, any primitive node;    -   (b) add to a target flow the primitive node identified in (a);    -   (c) identify, at the current top level of hierarchy in (a), any        complex node, each complex node containing at least one subflow        with one or more nodes interconnected by connectors;    -   (d) add to the target flow the at least one subflow in place of        the complex node identified in (c);    -   (e) re-establish connections between any nodes and subflows        added to the target flow, and maintain node terminal connections        such that any data flowing through the target flow is processed        as if through the source flow.

In an embodiment, the software further adapts the system, at (e), tore-establish connections between any nodes and subflows added to thetarget flow as follows:

-   -   a connection in the source flow that connects an origin        primitive node to a destination primitive node is re-established        in the target flow without modification;    -   a connection in the source flow that connects an origin        primitive node to a destination complex node is replaced in the        target flow by a re-established connection that connects the        origin primitive node to a node in each subflow that was        previously connected to an input node of the destination complex        node;    -   a connection in the source flow that connects an origin complex        node to a destination primitive node is replaced in the target        flow by a re-established connection that connects a node in each        subflow, that was previously connected to an output node of the        origin complex node, to the destination primitive node;    -   a connection in the source flow that connects an origin complex        node to a destination complex node is replaced in the target        flow by a re-established connection that connects a node in each        subflow that was previously connected to an output node in the        origin complex node, to a node in each subflow that was        previously connected to an input node in the destination complex        node.

In another aspect of the invention, there is provided a computerreadable medium containing computer executable code that when loaded ata computer system is operable for flattening a hierarchically structuredsource flow, the source flow including at least two levels of hierarchywith each level of hierarchy including one or more nodes interconnectedby connectors, the computer executable code adapting the computer systemto:

-   -   (a) identify, at a current top level of hierarchy in the source        flow, any primitive node;    -   (b) add to a target flow the primitive node identified in (a);    -   (c) identify, at the current top level of hierarchy in (a), any        complex node, each complex node containing at least one subflow        with one or more nodes interconnected by connectors;    -   (d) add to the target flow the at least one subflow in place of        the complex node identified in (c);    -   (e) re-establish connections between any nodes and subflows        added to the target flow, and maintain node terminal connections        such that any data flowing through the target flow is processed        as if through the source flow.

In another aspect of the invention, there is provided a computer systemfor flattening a hierarchically structured source flow, the source flowincluding at least two levels of hierarchy with each level of hierarchyincluding one or more nodes interconnected by connectors, the computersystem comprising:

-   -   (a) means for identifying, at a current top level of hierarchy        in the source flow, any primitive node;    -   (b) means for adding to a target flow the primitive node        identified in (a);    -   (c) means for identifying, at the current top level of hierarchy        in (a), any complex node, each complex node containing at least        one subflow with one or more nodes interconnected by connectors;    -   (d) means for adding to the target flow the at least one subflow        in place of the complex node identified in (c);    -   (e) means for re-establishing connections between any nodes and        subflows added to the target flow, and maintaining node terminal        connections such that any data flowing through the target flow        is processed as if through the source flow.

These and other aspects of the invention will become apparent from thefollowing more particular descriptions of exemplary embodiments of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the figures which illustrate exemplary embodiments of the invention:

FIG. 1 is a schematic block diagram of a computer system which mayprovide an operating environment for practicing exemplary embodiments ofthe invention;

FIG. 2 shows illustrative pseudo-code for a method in accordance with anembodiment of the invention;

FIG. 3 is a schematic block diagram showing an illustrativehierarchically structured flow containing complex nodes;

FIG. 4 is a schematic block diagram showing the hierarchicallystructured flow of FIG. 3 after an iteration of flattening;

FIG. 5 is a schematic block diagram showing the hierarchicallystructured flow of FIG. 4 after another iteration of flattening.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic block diagram of a computer system which mayprovide an operating environment for practicing exemplary embodiments ofthe invention. The computer system 100 may include a central processingunit (“CPU”) 102 connected to a storage unit 104 and to a random accessmemory (“RAM”) 106. The CPU 102 may process an operating system 101, aflow programming compiler 103, and a message broker 123 (described infurther detail below). The operating system 101, message broker 123 andcompiler 103 may be stored in the storage unit 104 and loaded into RAM106, as required. A user 107 may interact with the computer system 100using a video display 108 connected by a video interface 105, andvarious input/output devices such as a keyboard 110, mouse 112, and diskdrive 114 connected by an I/O interface 109. The disk drive 114 may beconfigured to accept computer readable media 116. The computer system100 may be network enabled via a network interface 111, allowing thecomputer system 100 to communicate with compatible computer systems (notshown) across a network. It will be appreciated that the computer system100 of FIG. 1 is illustrative, and is not meant to be limiting in termsof the type of system which may provide a suitable operating environmentfor practicing the present invention.

As will be described below, compiler 103 may be configured to flattenhierarchically structured flows in accordance with an embodiment of theinvention. Compiler 103 may also be configured to interact with messagebroker 123 so that a message may be transferred to and received fromanother system (not shown) via network interface 111. As an illustrativeexample, message broker 123 may comprise IBM's WebSphere BusinessIntegration Message Broker™ (WBIMB). WBIMB requires flattening ofhierarchically structured flows in order to broker a transaction betweentwo or more systems.

In accordance with an illustrative embodiment of the invention, compiler103 may be configured to flatten hierarchically structured flows usingthe following general approach:

I. First, load the source flow to be flattened. Define a temporarytarget flow for storing a new version of the source flow flattened byone hierarchical level. At a current top level of hierarchy of thesource flow, proceed as follows across the entire breadth of the flow:

-   -   a) If a node is a primitive node (i.e. does not contain a        subflow), simply add the primitive node to the target flow.    -   b) If a node is a complex node (i.e. contains a plurality of        nodes including at least one subflow), flatten the complex node        by one hierarchical level by adding the subflow(s) to the target        flow in place of the complex node.

II. In the target flow, re-establish connections between nodes asfollows:

-   -   a) A connection in the source flow that connects two primitive        nodes (origin and destination) is re-established in the target        flow without modification.    -   b) A connection in the source flow that connects an origin        primitive node to a destination complex node is replaced in the        target flow by a connection that connects the origin primitive        node to a node in each destination subflow that was previously        connected to an input node of the destination complex node.        Since each node can have multiple input or output terminals, the        node terminals that are used for connection to each node in the        target flow are the same as those used in the source flow.    -   c) A connection in the source flow that connects an origin        complex node to a destination primitive node is replaced in the        target flow by a connection that connects a node in each subflow        that was previously connected to an output node of the origin        complex node to the destination primitive node. Since each node        can have multiple input or output terminals, the node terminals        that are used for connection in the target flow are the same as        those used in the source flow.    -   d) A connection in the source flow that connects two complex        nodes (origin and destination) is replaced in the target flow by        a connection that connects a node in each subflow that was        previously connected to an output node in the origin complex        node, to a node in each subflow that was previously connected to        an input node in the destination complex node. Again, the node        terminals that are used for connection in the target flow are        the same as those used in the source flow.    -   e) While performing the above, check to see if any complex nodes        have been added to the target flow. If so, set a “flattened”        flag to false.

III. Once a particular level of hierarchy has been processed, check the“flattened” flag.

-   -   a) If the “flattened” flag indicator is true, then terminate the        flattening process. The target flow in the last iteration is the        flattened equivalent of the initial hierarchically structured        source flow, and can be deployed into the message broker 123        (e.g. for transfer to another system).    -   b) If the “flattened” flag indicator is false, repeat I and II        using the target flow as the new source flow and another defined        temporary target flow.

The general approach described above may also be expressed inillustrative pseudo-code 200, as shown in FIG. 2. Pseudo-code 200 beginsat line 201 with a main loop in which the initial hierarchicallystructured source flow described earlier is now referred to as“sampleFlow”. The main loop (line 201-line 231) continues for as long assampleFlow is not flat. As explained at comments line 202, and as shownat lines 203 and 204, the compiler (i.e. compiler 103 of FIG. 1) addsall primitive nodes from sampleFlow to a target flow referred to as“flatSampleFlow”.

At lines 206-216 (as explained at comment line 205), for each node insampleFlow that is a complex node, the compiler retrieves all nodescontained in the complex node and adds the nodes to the target flow(flatSampleFlow). At lines 211-214, if any node inside a flattenedcomplex node is also a complex node, then a flag“flatSampleFlow.flatStatus” is set to “false”. In this case, as noted atcomment line 213, at least one more iteration is needed beforesampleFlow is completely flattened.

At lines 219-230, as explained at comment lines 217 and 218, connectionsthat existed between nodes in sampleFlow are re-established inflatSampleFlow. More generally, a connection “aCon” is re-established independence upon the type of origin node (“originNode”) and the type ofdestination node (“destinationNode”) connected by the connection aCon.

At lines 219-220, where both the originNode and destinationNode are notcomplex nodes, a connection aCon is re-established without any change.

At lines 221-225, from the perspective of a connection aCon whosedestinationNode is a complex node, if the originNode is a primitivenode, connection aCon is re-established such that the originNode isconnected to a node in each subflow that was previously connected to an“auxiliary” input node (e.g. see references 332/342 in FIG. 3, below) ofthe destinationNode. Particular node terminal connections aremaintained. Here, the “auxiliary” input node simply provides aconnection point to a subflow or subflows within the complex node. Assuch, as the hierarchical structure is flattened, the input node may beeliminated.

For a connection aCon whose destinationNode is a complex node, if theoriginNode is not a primitive node (i.e. is a complex node), connectionaCon is re-established such that a node in each subflow that waspreviously connected to an “auxiliary” output node (e.g. see reference334/344 in FIG. 3, below) of the originNode is connected to a node ineach subflow that was previously connected to an “auxiliary” input nodeof the destinationNode. Here, again, the “auxiliary” output node simplyprovides a connection point to a subflow or subflows within the complexnode. As such, as the hierarchical structure is flattened, both inputnodes and output nodes may be eliminated.

At lines 226-230, from the perspective of a connection aCon whoseoriginNode is a complex node, if the destinationNode is a primitivenode, connection aCon is re-established such that a node in each subflowthat was previously connected to an “auxiliary” output node of theoriginNode is connected to the destinationNode. Particular node terminalconnections are maintained.

For a connection aCon whose originNode is a complex node, if thedestinationNode is not a primitive node (i.e. also a complex node),connection aCon is re-established such that a node in each subflow thatwas previously connected to an “auxiliary” output node in the originNodeis connected to a node in each subflow that was previously connected toan “auxiliary” input node in the destinationNode. (It will be seen thatthis simply repeats the case where both origin and destination nodes arecomplex, as at lines 226-230 above. Pseudo-code 200 is shown forillustrative purposes only and is not meant to be limiting.)

At line 231, if flag “flatSampleFlow.flatStatus” is “true” (i.e. thereare no more complex nodes, as determined at lines 206-216), pseudo-code200 exits the main loop, as sampleFlow is deemed to be completely flat.

Application of pseudo-code 200 to flatten a hierarchically structuredflow will now be explained in the context of an illustrative example.

EXAMPLE

FIG. 3 is a schematic block diagram showing an illustrativehierarchically structured source flow 300 (e.g. “sampleFlow” in FIG. 2)having an input 310 labeled “MQInput”, an output 320 labeled “MQOutput”,and two nested instances of another flow: complex node 330 labeled“Subflow_1_1”, and complex node 340 labeled “Subflow_1_2”.

In the illustrative example, input node 310 has three output terminals312 a-312 c, with output terminal 312 a connected to complex node 330 bya connector 350, and output terminal 312 b connected to complex node 340by another connector 350. Output terminal 312 c is not connected.Complex nodes 330 and 340 are both connected by connectors 350 to aninput terminal 321 of output node 320. (It will be understood that theseterminal connections are merely illustrative.)

Pseudo-code 200 starts by loading the initial source flow 300 of FIG. 3and considering each node in the top level of flow 300 for possibleaddition to a target flow (e.g. to the “flatSampleFlow” of FIG. 2).

As a first step, any primitive nodes that exist in the top level of thesource flow 300 are added to the target flow as is. In the illustrativeexample, both input 310 (MQInput) and output (MQOutput) are primitivenodes in the top level, and are added to the target flow in theirexisting form.

If a node is a complex node, as is the case with complex node 330(Subflow1 ₁₃ 1) and complex node 340 (Subflow1_2), the subflows that arenested inside these complex nodes are added to the target flow in placeof the complex nodes. In this example, complex node 330 includes an“auxiliary” input node 332, an “auxiliary” output node 334, and lowerlevel complex nodes 410 and 420. Similarly, complex node 340 includes an“auxiliary” input node 342, an “auxiliary” output node 344, and lowerlevel complex nodes 430 and 440. As the subflows 410, 420, 430, 440 areadded to the target flow, the connections 350 are re-established inaccordance with pseudo-code 200 in FIG. 2, depending on whether originand destination nodes are primitive or complex.

The results, after a first iteration of flattening, are shown in targetflow 400 in FIG. 4. As shown, complex nodes 410, 420, 430 and 440 havereplaced complex node 330 and complex node 340. As well, connectors 350have been re-established such that, for example, output terminal 312 aof input node 310 is now connected directly to each of complex nodes 410and 420 via “auxiliary” input node 512 and “auxiliary” input node 522respectively. Similarly, complex nodes 410 and 420 are in turn connecteddirectly to input terminal 321 of output 320 via “auxiliary” output node514 and “auxiliary” output node 524 respectively. Input node 332 andoutput node 334 previously shown inside complex node 330 are no longernecessary due to the re-established connections as described above, andare not added to the target flow 400.

Similarly, output terminal 312 b of input 310 is now connected directlyto complex nodes 430 and 440. Complex nodes 430 and 440 are in turnconnected directly to input terminal 321 of output 320. Due to thesere-established connections, input node 342 and output node 344 are nolonger necessary, and are not added to the target flow 400.

As will be seen, while the target flow 400 has been flattened onehierarchical level from the source flow 300, due to re-establishment ofthe node terminal connections as described, data flowing through eitherthe source flow 300 or the target flow 400 will be processed in the sameway.

After all complex nodes at the top hierarchical level have beenflattened by one level, if the target flow is not completely flat, theprocess may be repeated. Thus, the target flow 400 may become a newsource flow, and a new target flow 500 (FIG. 5) may be defined.

Applying pseudo-code 200, any primitive nodes at the top level (i.e.input 310 and output 320) are again added to the target flow in theirexisting form. Any complex nodes are again replaced by subflows in thetarget flow, with connections re-established as per pseudo-code 200.Thus, complex nodes 410, 420, 430 and 440 are replaced by “subflow”nodes 510, 520, 530 and 540, which in this illustrative example performa particular “compute” function, whatever that may be.

In the target flow shown in FIG. 5, connectors 350 are againre-established such that output terminal 312 a of input 310 is connecteddirectly to input terminal 511 of node 510, and to input terminal 521 ofnode 520. Nodes 510 and 520 are in turn connected directly to inputterminal 321 of output 320. Similarly, output terminal 312 b of input310 is connected directly to input terminal 531 of node 530, and toinput terminal 541 of node 540. Output terminals 513 a, 523 a, 533 a,and 543 a of nodes 530 and 540 are in turn connected directly to inputterminal 321 of output 320.

As seen in FIG. 5, the connections to terminals 511 and 513 a of node510 have been maintained from that shown in FIG. 4. Similarly, theconnections to terminals 521 and 523 a of node 520 have been maintained;the connections to terminals 531 and 533 a of node 530 have beenmaintained; and the connections to terminals 541 and 543 a of node 540have been maintained. Output terminals 513 b, 523 b, 533 b, and 543 bremain unconnected.

As a result of re-establishment of the terminal connections as describedabove, input nodes 512, 522, 532, 542 and output nodes 514, 524, 534,544 previously shown in complex nodes 410, 420, 430, 440 are no longernecessary, and are not added to the new target flow 500.

While the target flow 500 has been flattened another level from thesource flow (i.e. the previous target flow) 400, due to re-establishmentof terminal connections as described above, data flow through the targetflow 500 will be processed as if through the source flow 400.

As each node 510, 520, 530 and 540 is a primitive node, and there are nofurther complex nodes in the target flow 500, the flow has beencompletely flattened. Consequently, the pseudo-code 200 of FIG. 2 mayexit the main loop and end.

The breadth-first approach to flattening hierarchically structured flowsas described above allows flattening of a hierarchically structured flowin an iterative manner, based on the number of levels of hierarchy, andindependent of the number of complex nodes at each level of hierarchy.

Advantageously, for flows that are generally broad, with a limitednumber of hierarchical levels, the breadth-first approach to flatteningas described above provides an efficient alternative to known flatteningtechniques, which may otherwise require repeated loading of flows andsubflows at each level of hierarchy in order to flatten a flow. In manycommon flow programming applications, such as transactions betweenfinancial institutions, it has been found that the breadth-firstapproach in accordance with the teachings of the present invention maybe more suitable, as the flow models are typically broad, with a limitednumber of hierarchical levels. Of course, the flattening techniquetaught by the present invention may be used for numerous otherapplications.

The invention may be implemented as computer readable medium containingcomputer executable which, when combined or loaded on a computer system,performs the method steps of the invention. Such computer readablemedium may include, but is not limited to, CD-ROMs, diskettes, tapes,hard drives, and computer RAM or ROM, or any solid or fluid transmissionmedium, magnetic or optical, or the like, for storing signals readableby a machine for controlling the operation of a general or specialpurpose programmable computer according to the method of the inventionand/or to structure its components in accordance with a system of theinvention.

While various illustrative embodiments of the invention have beendescribed above, it will be appreciated by those skilled in the art thatvariations and modifications may be made. Thus, the scope of theinvention is defined by the following claims.

1. A computer system-implemented method of flattening a hierarchicallystructured source flow, said source flow including at least two levelsof hierarchy with each level of hierarchy including one or more nodesinterconnected by connectors, said computer system-implemented methodcomprising: (i) identifying, at a current top level of hierarchy in saidsource flow, any primitive node; (ii) adding to a target flow saidprimitive node identified in (i); (iii) identifying, at said current toplevel of hierarchy in (i), any complex node, each complex nodecontaining at least one subflow with one or more nodes interconnected byconnectors; (iv) adding to said target flow said at least one subflow inplace of said complex node identified in (iii); (v) re-establishingconnections between any nodes and subflows added to said target flow,and maintaining node terminal connections such that any data flowingthrough said target flow is processed as if through said source flow. 2.The computer system-implemented method of claim 1, further comprising:(vi) identifying whether there are remaining complex nodes in saidtarget flow, and if so, providing an indication thereof.
 3. The computersystem-implemented method of claim 2, further comprising: (vii)responsive to said indication of remaining complex nodes in said targetflow, defining said target flow to be a new source flow, defining a newtarget flow, and repeating each of (i) to (v) for said new source flow.4. The computer system-implemented method of claim 1, wherein, at (v),re-establishing connections between any nodes and subflows added to saidtarget flow proceeds as follows: a connection in said source flow thatconnects an origin primitive node to a destination primitive node isre-established in said target flow without modification; a connection insaid source flow that connects an origin primitive node to a destinationcomplex node is replaced in said target flow by a re-establishedconnection that connects said origin primitive node to a node in eachsubflow that was previously connected to an input node of saiddestination complex node; a connection in said source flow that connectsan origin complex node to a destination primitive node is replaced insaid target flow by a re-established connection that connects a node ineach subflow that was previously connected to an output node of saidorigin complex node to said destination primitive node; a connection insaid source flow that connects an origin complex node to a destinationcomplex node is replaced in said target flow by a re-establishedconnection that connects a node in each subflow that was previouslyconnected to an output node of said origin complex node, to a node ineach subflow that was previously connected to an input node of saiddestination complex node.
 5. The computer system-implemented method ofclaim 4, further comprising: (vi) identifying whether there areremaining complex nodes in said target flow, and if so, providing anindication thereof.
 6. The computer system-implemented method of claim5, further comprising: (vii) responsive to said indication of remainingcomplex nodes in said target flow, defining said target flow to be a newsource flow, defining a new target flow, and repeating each of (i) to(v) for said new source flow.
 7. A computer system comprising aprocessor and computer readable memory, said memory storing software forflattening a hierarchically structured source flow, said source flowincluding at least two levels of hierarchy with each level of hierarchyincluding one or more nodes interconnected by connectors, said softwareadapting said system to: (a) identify, at a current top level ofhierarchy in said source flow, any primitive node; (b) add to a targetflow said primitive node identified in (a); (c) identify, at saidcurrent top level of hierarchy in (a), any complex node, each complexnode containing at least one subflow with one or more nodesinterconnected by connectors; (d) add to said target flow said at leastone subflow in place of said complex node identified in (c); (e)re-establish connections between any nodes and subflows added to saidtarget flow, and maintain node terminal connections such that any dataflowing through said target flow is processed as if through said sourceflow.
 8. The computer system of claim 7, wherein said software furtheradapts said system to: (f) identify whether there are remaining complexnodes in said target flow, and if so, provide an indication thereof. 9.The computer system of claim 8, wherein said software further adaptssaid system to: (g) responsive to said indication of remaining complexnodes in said target flow, define said target flow to be a new sourceflow, define a new target flow, and repeat each of (a) to (e) for saidnew source flow.
 10. The computer system of claim 7, wherein saidsoftware further adapts said system, at (e), to re-establish connectionsbetween any nodes and subflows added to said target flow as follows: aconnection in said source flow that connects an origin primitive node toa destination primitive node is re-established in said target flowwithout modification; a connection in said source flow that connects anorigin primitive node to a destination complex node is replaced in saidtarget flow by a re-established connection that connects said originprimitive node to a node in each subflow that was previously connectedto an input node of said destination complex node; a connection in saidsource flow that connects an origin complex node to a destinationprimitive node is replaced in said target flow by a re-establishedconnection that connects a node in each subflow that was previouslyconnected to an output node of said origin complex node to saiddestination primitive node; a connection in said source flow thatconnects an origin complex node to a destination complex node isreplaced in said target flow by a re-established connection thatconnects a node in each subflow that was previously connected to anoutput node of said origin complex node, to a node in each subflow thatwas previously connected to an input node of said destination complexnode.
 11. The computer system of claim 10, wherein said software furtheradapts said system to: (f) identify whether there are remaining complexnodes in said target flow, and if so, provide an indication thereof. 12.The computer system of claim 11, wherein said software further adaptssaid system to: (g) responsive to said indication of remaining complexnodes in said target flow, define said target flow to be a new sourceflow, define a new target flow, and repeat each of (a) to (e) for saidnew source flow.
 13. A computer readable medium containing computerexecutable code that when loaded at a computer system is operable forflattening a hierarchically structured source flow, said source flowincluding at least two levels of hierarchy with each level of hierarchyincluding one or more nodes interconnected by connectors, said computerexecutable code adapting said computer system to: (a) identify, at acurrent top level of hierarchy in said source flow, any primitive node;(b) add to a target flow said primitive node identified in (a); (c)identify, at said current top level of hierarchy in (a), any complexnode, each complex node containing at least one subflow with one or morenodes interconnected by connectors; (d) add to said target flow said atleast one subflow in place of said complex node identified in (c); (e)re-establish connections between any nodes and subflows added to saidtarget flow, and maintain node terminal connections such that any dataflowing through said target flow is processed as if through said sourceflow.
 14. The computer readable medium of claim 13, wherein saidcomputer executable code further adapts said system to: (f) identifywhether there are remaining complex nodes in said target flow, and ifso, provide an indication thereof.
 15. The computer readable medium ofclaim 14, wherein said computer executable code further adapts saidsystem to: (g) responsive to said indication of remaining complex nodesin said target flow, define said target flow to be a new source flow,define a new target flow, and repeat each of (a) to (e) for said newsource flow.
 16. The computer readable medium of claim 14, wherein saidcomputer executable code further adapts said system, at (e) tore-establish connections between any nodes and subflows added to saidtarget flow as follows: a connection in said source flow that connectsan origin primitive node to a destination primitive node isre-established in said target flow without modification; a connection insaid source flow that connects an origin primitive node to a destinationcomplex node is replaced in said target flow by a re-establishedconnection that connects said origin primitive node to a node in eachsubflow that was previously connected to an input node of saiddestination complex node; a connection in said source flow that connectsan origin complex node to a destination primitive node is replaced insaid target flow by a re-established connection that connects a node ineach subflow that was previously connected to an output node of saidorigin complex node to said destination primitive node; a connection insaid source flow that connects an origin complex node to a destinationcomplex node is replaced in said target flow by a re-establishedconnection that connects a node in each subflow that was previouslyconnected to an output node of said origin complex node, to a node ineach subflow that was previously connected to an input node of saiddestination complex node.
 17. The computer readable medium of claim 16,wherein said computer executable code further adapts said system to: (f)identify whether there are remaining complex nodes in said target flow,and if so, provide an indication thereof.
 18. The computer readablemedium of claim 17, wherein said computer executable code further adaptssaid system to: (g) responsive to said indication of remaining complexnodes in said target flow, define said target flow to be a new sourceflow, define a new target flow, and repeat each of (a) to (e) for saidnew source flow.
 19. A computer system for flattening a hierarchicallystructured source flow, said source flow including at least two levelsof hierarchy with each level of hierarchy including one or more nodesinterconnected by connectors, said computer system comprising: (a) meansfor identifying, at a current top level of hierarchy in said sourceflow, any primitive node; (b) means for adding to a target flow saidprimitive node identified in (a); (c) means for identifying, at saidcurrent top level of hierarchy in (a), any complex node, each complexnode containing at least one subflow with one or more nodesinterconnected by connectors; (d) means for adding to said target flowsaid at least one subflow in place of said complex node identified in(c); (e) means for re-establishing connections between any nodes andsubflows added to said target flow, and maintaining node terminalconnections such that any data flowing through said target flow isprocessed as if through said source flow.
 20. The computer system ofclaim 19, wherein said system includes means to re-establish connectionsbetween any nodes and subflows added to said target flow as follows: aconnection in said source flow that connects an origin primitive node toa destination primitive node is re-established in said target flowwithout modification; a connection in said source flow that connects anorigin primitive node to a destination complex node is replaced in saidtarget flow by a re-established connection that connects said originprimitive node to a node in each subflow that was previously connectedto an input node of said destination complex node; a connection in saidsource flow that connects an origin complex node to a destinationprimitive node is replaced in said target flow by a re-establishedconnection that connects a node in each subflow that was previouslyconnected to an output node of said origin complex node to saiddestination primitive node; a connection in said source flow thatconnects an origin complex node to a destination complex node isreplaced in said target flow by a re-established connection thatconnects a node in each subflow that was previously connected to anoutput node of said origin complex node, to a node in each subflow thatwas previously connected to an input node of said destination complexnode.
 21. The computer system of claim 20, further comprising: (f) meansfor identifying whether there are remaining complex nodes in said targetflow, and if so, providing an indication thereof.
 22. The computersystem of claim 21, further comprising: (g) means, responsive to saidindication of remaining complex nodes in said target flow, for definingsaid target flow to be a new source flow, defining a new target flow,and repeating each of (a) to (e) for said new source flow.